Prompt steals focus after search completes

[jdanbrown]

Repro:

1. Search a large project that takes many seconds to complete
2. Before the search completes, start moving the cursor through the search results
3. When the search completes, notice that the focus jumps back to the prompt

This is confusing and disruptive, particularly in large projects where the search always takes a long time to complete and you don't want to have to wait for completion every time before navigating the results.

(Thanks for the great package!)